Answer:
In order to understand the Reformed Baptist Church, we need to answer two preliminary questions: 1) What does it mean to be Baptist? 2) What does it mean to be Reformed?

To be Baptist is to be part of a church or denomination that, broadly speaking, holds to adult believer baptism (typically by full immersion) following a credible statement of faith as the only biblically acceptable way to administer the ordinance of baptism as commanded by our Lord in his Great Commission (Matthew 28:19–20). This is the view called credobaptism (“believer” baptism), which is held over against the view of paedobaptism (“infant” baptism) that is commonly practiced by Roman Catholics, Eastern Orthodox, Anglicans, Lutherans, Presbyterians, and many continental Reformed churches.

Baptists also generally believe in the autonomy of the local congregation over the more hierarchically structured denominations such as Roman Catholicism (which is based on an episcopal model of church government) and Presbyterianism (which is based on a presbyterian model of church government).

Within this broad category there are many different types of Baptists who hold various views on soteriology (doctrine of salvation) and ecclesiology (church structure and governance). Some fundamentalist Baptist groups hold that the King James Version of the Bible is the only true, inspired version of the Bible in the English language. Other Baptist groups are so theologically liberal that they fall outside the boundaries of what is generally accepted as orthodox. All this to say that Baptists come in many different shapes and sizes, but nominally they are all unified on the doctrine of adult believer baptism.

Baptist history is also a bit difficult to trace. There are some Baptist groups that claim the Baptist tradition can be traced in an unbroken line back to New Testament times, somewhat akin to the Roman Catholic tradition of papal succession. Others claim that, while there was not an unbroken chain of Baptist churches going all the way back to New Testament times, there was a continuity of Baptist forms of faith going all the way back to the earliest beginnings of the church. The most commonly accepted view holds that Baptist tradition is traced back to the English Separatist movement of the early 17th century. The English Separatists were a group of individuals who were unsatisfied with the changes made during the English Reformation, which was part of the larger Reformation movement sweeping the Continent, and hence they separated from the Church of England. From this Separatist movement, two strains of Baptists emerged—General Baptists and Particular Baptists. This leads us to our second question, noted above: What does it mean to be Reformed?

Generally speaking, to be Reformed means to have one’s roots in the Protestant Reformation of the 16th and 17th centuries. The Reformers were those who protested against certain abuses within the Roman Catholic Church. It is often said that the Protestant Reformation had both a formal cause and a material cause. The material cause of the Reformation (i.e., the particulars of the dispute) was over what became the doctrine of justification by grace alone, through faith alone in Christ alone. In other words, the debate centered on the question of how a man is made right before God. Rome’s basic answer to that question is that grace, faith, and Christ are all necessary, but they are, in and of themselves, not sufficient. The Reformers argued that grace, faith, and Christ are both necessary and sufficient.

The formal cause of the Reformation was the question of authority. What is the ultimate authority for the Christian in matters of faith and practice? For Rome, the answer is both Scripture and tradition. However, since, according to its dogma, the Roman Catholic Church is the source of both Scripture and tradition, as well as the infallible interpreter of both, the matter of authority essentially boils down to the Catholic Church alone. The Reformers believed that the Scriptures alone were the sole infallible rule for Christian faith and practice; hence the Bible is the ultimate authority in these matters. All other lesser authorities—church councils, synods, and church declarations—are only authoritative insofar as they conform to Scripture.

Inasmuch as Baptists are Protestant, they are Reformed in this general sense. However, there is a more specific sense of the word Reformed, and this is more germane to our discussion. Reformed in the more narrow sense refers to those groups that follow in the theological footsteps of John Calvin—in particular his doctrine of salvation. This is what separates the General Baptists from the Particular Baptists. The General Baptists are so called because they hold to a belief of general atonement—Jesus died to make all men, in a universal sense, savable. Particular Baptists hold to the Calvinistic understanding that Jesus died only for the elect, and He died to actually secure their salvation, i.e., particular atonement. Reformed Baptists flow out of this Particular Baptist stream.

Today there is no official Reformed Baptist denomination, but there are several federations of Reformed Baptist churches, such as the Association of Reformed Baptist Churches in America (ARBCA). Most Reformed Baptist churches subscribe to the London Baptist Confession of Faith (1689) as their doctrinal standards; the 1689 LBCF is essentially the Westminster Confession of Faith reworded as it pertains to baptism. Some notable Reformed Baptists in history are John Bunyan, William Carey, and Charles Spurgeon.